Antifogging and stabilizing agents for photography



rates The present invention relates to photographic materials comprising light-sensitive silver halide emulsions. More particularly, this invention is directed to stabilized silver halide emulsions which have less tendency to fog and which still possess substantially the same light sensitivity.

It is well established that light-sensitive emulsions such as gelatin-silver halide emulsions are subject to fogging. Fogging in general, and chemical fogging in particular, may be defined as a uniform deposit of silver extending over and either partially or wholly obliterating the image and is caused in a number of ways, namely, the nature of the emulsion, its age and the conditions under which it has been stored, the nature of the developer, impurities in the developing solution and the time and temperature of the development. Additionally, chemical fogging is promoted when such active agents as metal are employed in a concentrated solution or are used in the presence of an excess of alkali. Similarly, the oxidation of certain developing agents such as metol and and hydroquinone exerts a powerful fogging action.

Thus, it is an object of the present invention to provide light-sensitive silver halide emulsions which are stabilized against the formation of fog by the addition thereto of antifogging agents which tend to prevent the formation of chemical fogs and which suffer little or no lowering of light sensitivity thereby.

We have discovered that the above object is readily accomplished by intimately associating with silver halide emulsions compounds of the following general formula:

wherein X represents a halogeno radical such as chloro, bromo or iodo radicals and Y represents members selected from the group consisting of O, S, and NH.

Representative compounds characterized by the general formula supra which deserve special mention as suitable 2-chloromethyl-benzthiazole iatet i fi'llhlm- Patenteol Sept. 6, 1966 2-bromomethyl-benzoxazole 2-iodomethyl-benzoxazole The antifogging agents which have been found to impart such beneficial etfects to light-sensitive silver halide emulsions for the prevention of fogging and stabilization of said emulsions can be conveniently prepared in accordance with known procedures such as described in J. Org. Chem. 4, 14 (1938). For example, Z-chloromethylbenzimidazole is prepared by reacting 10.8 grams (0.1 mole) of O-phenylenediamine, 14.2 grams of chloroacetic acid and cc. of 4 N hydrochloric acid under reflux for 45 minutes. The reaction mixture is allowed to stand overnight and then diluted with 200 cc. of water, after which the reaction mixture was filtered and cooled. After rapid agitation of the reaction mixture, it was carefully neutralized with aqueous ammonium hydroxide (50:70). A black solid precipitate was then collected, dissolved in dioxane: treated with diarcoal and crystallized at room temperature overnight. There was provided 5 grams of a light tan solid, which melts at 149l50 C.

Beneficial effects in fog reduction are obtained when solutions of the antifoggant are incorporated into the silver halide emulsions as ripening finals or as coating finals. Ripening finals are added during the ripening or the sensitivity increasing stage of the emulsion-making process whereas coating finals are added to the silver halide emulsion just prior to the coating of the emulsion on a suitable support such as, for example, paper, glass or film, when the emulsion has nearly obtained its maximum sensitivity.

The addition of the an-tifoggants can be made before, during or after the addition of the soluble silver salt to the soluble halide in the presence of a suitable carrier or colloid such as gelatin, polyvinyl alcohol, solubilized casein, albumin and the like.

If desired, the antifoggants of the present invention can also be employed as components of the developing solution.

The amount of antifogging agent employed as additives to the light sensitive emulsions varies from about 5.0 to about 500 milligrams of antifoggant per 0.6 mole of silver halide. When the antifogging agents are employed as ripening finals it has been found advantageous to employ them in amounts in the range of from about 5.0 to about 50.0 milligrams per 0.6 mole of silver halide whereas when the antifogging agents are employed in coating finals it has been found advantageous to employ amounts in the range of from about 25.0 to about 500 milligrams of antifoggant per 0.6 mole of silver halide. Obviously, the development of optimum characteristics within the ranges set forth above will depend in part upon the type of emulsion employed and can be readily determined in each case. The antifoggants can be employed also in various kinds of photographic emulsions such as n0nsensitized emulsions, orthochromatic emulsions, panchromatic emulsions, X-ray emulsions, paper emulsions, color emulsions and the like.

In some cases, it has been found advantageous to apply the antifogging agents of the invention in adjacent layers, for example, in a separate undercoating layer on in the antiabrasion gelatine surface. Alternatively, it has been found advantageous in some cases, to apply the antifogging agents of the invention in one or all processing baths or in preand post-baths.

It has also been found that the antifogging agents of the invention can be compatibly employed in combination with other known antifoggants and stabilizers with sulfur-reduction and metal-, and noble metal sensitizers as Well as in combination with polyoxyalkylene polyols, their derivatives; polyvinylpyrolidones and other accelerators.

The following examples will serve to illustrate the practice of the invention:

Example I A silver halide emulsion in gelatin containing 2% silver iodide and 98% silver bromide was prepared in a conventional manner and brought up to its maximum light sensitivity. It was then readied for coating, finals were added such as sensitizing dyes, and hardening agents. A 1.0% solution of 2-chloromethyl-benzimidazole Was prepared and added to the emulsion as an antifoggant and stabilizer. The emulsion samples contained about 0.6 mole of silver halide. The so-prepared emulsion samples were coated on a suitable cellulose ester base and dried. Samples of these film coatings were then exposed to a Type IB Sensitometer and developed in a developer of the following composition:

Oven Test 4 days at 35 Cfind 13% rel.

umi Quantity of Compound Added Relative Speed Fog at 6 Development Relative Oven Fog Speed at 6 Development U 100 l1 23 50 100 mg 100 09 13 100 200 mg .t 100 09 13 100 Example H Example I was repeated using 2-bromomethyl-benzirnidazole as the antifoggant instead of 2-chloromethyl-benzimidazole. The results of the experiment indicated general agreement with the results obtained in Example 1.

Example III Example I was repeated using 2-iodomethyl-benzimidazole as the antifoggant instead of 2-chloromethylbenzimidazole. The results obtained were similar to those obtained in Example 1.

Various modifications of the invention will occur to persons skilled in the art. Thus, it is evident in lieu of the compounds of the specific examples, any of the coinpounds mentioned above can be employed with similar results. Therefore, it is not intended that the invention be limited in the patent granted except as necessitated by the appended claims.

What is claimed is:

1. A light sensitive photographic material comprising a light sensitive silver halide emulsion, a carrier therefor and an antifoggant characterized by the general formula:

all

wherein X represents a halogeno radical selected from the group consisting of chlorine, bromine and iodine, and Y represents members selected from the group consisting of O, S and NH.

2. The material as defined in claim 11 wherein the antifoggant is located in the silver halide emusion.

3. The material as defined in claim 1 wherein the antifoggant is located in a layer adjacent the silver halide emulsion.

4. A light sensitive photographic material comprising a light sensitive silver halide emulsion, a carrier therefor, said emulsion containing, as an antifoggant, 2- chloromethyl-benzimidazole.

5. A light sensitive photographic material comprising a light sensitive silver halide emulsion, a carrier therefor, said emulsion containing, as an antifoggant, 2- bromomethyl-benzimidazole.

6. A light sensitive photographic material comprising a light sensitive silver halide emulsion, a carrier therefor, said emulsion containing, as an antifoggant, 2- chloromethyl-benzthiazole.

7. A light sensitive photographic material comprising a light sensitive silver halide emulsion, a carrier therefor, said emulsion containing, as an antifoggant, 2- bromomethyl-benzoxazole.

8. A light sensitive photographic material comprising a light sensitive silver halide emulsion, a carrier there for, said emulsion containing, as an antifoggant, 2- iodomethyl-benzoxazole.

9. A process of minimizing and preventing fog in light sensitive silver halide materials comprising a base having a light sensitive silver halide emulson thereon, which comprises exposing said emulsion to light and developing the same in the presence of an antifoggant characterized by the general formula:

wherein X represents a halogeno radical selected from the group consisting of chlorine, bromine and iodine, and Y represents members selected from the group consisting of O, S and NH.

10. A photographic developer containing a developing agent and an antifoggant characterized by the general formula:

CCIIzX wherein X represents a halogeno radical selected from the group consisting of chlorine, bromine and iodine, and Y represents members selected from the group consisting of O, S and NH.

References Cited by the Examiner UNITED STATES PATENTS 2,131,038 9/1938 Brooker et a1 96-109 2,728,667 12/1955 Knott et al 96l09 3,023,103 2/1962 Dersch et al. 96l09 3,189,453 6/1965 Herz et a1. 96l09 OTHER REFERENCES Bloom et al., Journal Organic Chemistry, vol. 4, pages 14-19 (1939).

NORMAN G. TORCHIN, Primary Examiner.

LOUISE P. QUAST, Examiner.

J. T. BROWN, I. RAUBITSCHEK, Assistant Examiners. 

10. A PHOTOGRAPHIC DEVELOPER CONTAINING A DEVELOPING AGENT AND AN ANTIFOGGANT CHARACTERIZED BY THE GENERAL FORMULA: 